The present invention relates to the field of mass storage devices. More particularly, this invention relates to improving the tribological performance of bearings in a disc drive.
One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically housed within a small ceramic block. The small ceramic block, also referred to as a slider, passes over the disc in a transducing relationship with the disc. The transducer can be used to read information representing data from the disc or write information representing data to the disc. When the disc is operating the disc is usually spinning at relatively high revolutions per minute (RPM). These days common rotational speeds are up to 10,000 RPM. Higher rotational speeds are contemplated for the future. The small ceramic block, or slider, is usually aerodynamically designed so that it flies over the disc. The best performance of the disc drive results when the ceramic bock is flown as closely to the surface of the disc as possible. Today""s small ceramic block or slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the slider and the disc is very small. The fly height is the thickness of the air lubrication film or the distance between the disc surface and the transducing head. Currently, fly heights are about 0.5-1.0 micro inches. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the memory disc. Disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The memory disc rotates upon a spindle. The spindle assembly contains bearings such as hydrodynamic bearings or ball and socket bearings. Bearings are generally used in numerous applications to allow two surfaces to be supported, guided, or rotated in relation to each other. Hydrodynamic bearings are bearings in which a fluid barrier, such as a lubricant or air, is created between the stator or stationary bearing surface and the rotor or dynamic bearing surface which faces the stator surface. One problem encountered using hydrodynamic bearings is that, during start up of the bearing, before the fluid barrier is formed, machined imperfections on the two facing bearing surfaces, such as machining burrs and imperfect flatness, come into contact with each other. This localized pressure causes a jerky and unpredictable rotation. Also, when the bearing slows down and the two surfaces come into contact again, the burrs can cause unpredictable behavior and may also cause further damage to the other surface.
Ball and socket bearings are bearings in which a ball rotates within a socket and a boundary lubricated interface is developed between the two surfaces. Ball and socket bearings are used in many devices beyond disc drives such as in diverse machinery, automobiles, and knee replacement joints. One problem encountered using ball and socket bearings is that, before the lubricant boundary is formed, the machined imperfections on the surfaces of the ball and the socket strike each other during a period called break-in. The broken material then causes Lewis acids to form, which cause a break down of the lubricant itself. Another problem with bearings in general is that when the stator surface and the rotor surface are made out of different materials, the tribological performance is unpredictable.
A general solution to these problems is to reduce the machined imperfections on the bearing surfaces. However, it is not technologically feasible to machine surfaces that are theoretically perfect and without defects. At a microscopic level, protuberances and imperfections are always present and inherent in the materials. Also, from an economic perspective, it is expensive to attempt to machine surfaces with such minuscule tolerance for error. Furthermore, even if two surfaces were theoretically flat, the problem of inherent static friction at start up would still be a problem since the surfaces would be in complete contact with each other, and this real surface contact would lead to a high localized pressure throughout the contacting surfaces. Thus, a flat surface itself can lead to unpredictable performance.
Thus, what is needed is an economically feasible system that permits the smooth and predictable takeoff and landing of hydrodynamic bearing surfaces, avoids the break-in period of ball and socket bearings, and permits bearing designers to use dissimilar bearing materials while achieving predictable performance.
The present invention provides a system for minimizing contact between the surfaces of bearings at rest. Thus, there is a smooth and predictable take-off period and landing period for hydrodynamic bearings, and a clean break-in period for ball and socket bearings. The system includes a first bearing surface which moves against a second bearing surface, the first surface having a distribution of diamond-like carbon (DLC) pads or bumps. The DLC pads are at a height that is approximately the height of the roughness or imperfections of the surfaces. Thus, the pads help keep the bearing surfaces from coming in contact. The DLC pads are distributed over the bearing surface such that there are enough pads to provide support to the other bearing surface, yet not so many that the pads form a continuous surface and thereby undesirably effect the tribological performance of the bearing.
In further embodiments, the system provides a hydrodynamic bearing having a stator member having hydrodynamic grooves and DLC pads on a thrust plate surface, and a rotor member having an end facing the thrust plate. In another embodiment of the system, a ball and socket bearing having DLC pads is provided.
The present system advantageously provides a system to keep hydrodynamic and other bearing surfaces from coming in contact when the rotor bearing surface is at rest or at a slow speed. This provides the advantage that the imperfections on the surfaces will not come in contact with the other bearing surface and cause unpredictable performance or hinder development of the hydrodynamic boundary.